27/20: Difference between revisions
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In [[5-limit]] [[just intonation]], '''27/20''', the '''classic acute fourth''', is an interval measuring about 519.6{{cent}}. It differs from the [[4/3]] perfect fourth by [[81/80]] (about 21.5{{cent}}), the syntonic comma. It arises naturally in JI as (for instance) the difference between a 5-limit major third and a stack of five [[3/2]] perfect fifths, or as the interval between [[10/9]] and [[3/2]]. In [[12edo]] and [[meantone]] systems, this interval would be no different from 4/3, as the syntonic comma is tempered out. 27/20 has been described as a "wolf" interval, implying that it "howls", as compared to simpler intervals within the 5-limit such as [[5/4]] and [[9/8]]. Although in a 5-limit context it is traditionally avoided, it can be an essential interval in a harmonic context of higher complexity, where it may be admired for its bright and active character and its distinctness from 4/3. | In [[5-limit]] [[just intonation]], '''27/20''', the '''classic acute fourth''', is an interval measuring about 519.6{{cent}}. It differs from the [[4/3]] perfect fourth by [[81/80]] (about 21.5{{cent}}), the syntonic comma. It arises naturally in JI as (for instance) the difference between a 5-limit major third and a stack of five [[3/2]] perfect fifths, or as the interval between [[10/9]] and [[3/2]]. In [[12edo]] and [[meantone]] systems, this interval would be no different from 4/3, as the syntonic comma is tempered out. 27/20 has been described as a "wolf" interval, implying that it "howls", as compared to simpler intervals within the 5-limit such as [[5/4]] and [[9/8]]. Although in a 5-limit context it is traditionally avoided, it can be an essential interval in a harmonic context of higher complexity, where it may be admired for its bright and active character and its distinctness from 4/3. | ||
== Approximation == | == Approximation == | ||
{{Interval edo approximation|27/20} | |||
== See also == | == See also == | ||
* [[40/27]] – its [[octave complement]] | * [[40/27]] – its [[octave complement]] | ||
Revision as of 13:06, 3 November 2025
| Interval information |
classic acute fourth
[sound info]
In 5-limit just intonation, 27/20, the classic acute fourth, is an interval measuring about 519.6 ¢. It differs from the 4/3 perfect fourth by 81/80 (about 21.5 ¢), the syntonic comma. It arises naturally in JI as (for instance) the difference between a 5-limit major third and a stack of five 3/2 perfect fifths, or as the interval between 10/9 and 3/2. In 12edo and meantone systems, this interval would be no different from 4/3, as the syntonic comma is tempered out. 27/20 has been described as a "wolf" interval, implying that it "howls", as compared to simpler intervals within the 5-limit such as 5/4 and 9/8. Although in a 5-limit context it is traditionally avoided, it can be an essential interval in a harmonic context of higher complexity, where it may be admired for its bright and active character and its distinctness from 4/3.
Approximation
{{Interval edo approximation|27/20}